Metabolic syndrome is a cluster of metabolic abnormalities that identifies people at risk of diabetes and cardiovascular disease, whereas non-alcoholic fatty liver disease (NAFLD) is defined as a disorder with excess fat in the liver due to non-alcoholic causes. Two key components of metabolic syndrome, glucose and triglycerides, are overproduced by the fatty liver. The liver is therefore a key determinant of metabolic abnormalities. The prevalence of both metabolic syndrome and NAFLD increases with obesity. Other acquired causes for both disorders include excessive intake of simple sugars and physical inactivity. Both disorders predict type 2 diabetes, cardiovascular disease, non-alcoholic steatohepatitis (NASH), and hepatocellular carcinoma. Because metabolic syndrome can be defined in many different ways, NAFLD might be a more direct predictor of these diseases. Half of people with NAFLD carry at least one variant (G) allele at rs738409 in the PNPLA3 gene, which is associated with high liver fat content. Steatosis in PNPLA3-associated NAFLD is not accompanied by features of metabolic syndrome. All forms of NAFLD increase the risk of NASH, cirrhosis, and hepatocellular carcinoma.
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